This disclosure contemplates an improved identification wristband, bracelet, patch, headband, necklace, card, sticker, or other wearable appliance, which for the sake of convenience, are collectively referred to as a “band” or as an “identification appliance”. Identification bands have become a convenient and effective way of identifying people without permanently marking them. A principle advantage of a band is that it is ultimately removable. Identification bands typically consist of a flexible wrist strap having a length greater than its width, and a closure or securement device for attaching and maintaining the band securely around the wearer's wrist. A portion of the band may be used for imprinting or otherwise attaching identification or other information regarding the wearer. Bar codes, radio frequency identification (RFID) devices and the like may also be used to store and transfer information associated with the band and the associated person or object. For example, RFID devices includes those which operate in the frequency in the range 30 kilohertz (kHz) to 300 Gigahertz (GHz). Various band constructions, attachments and other features including the storage of electronic data and RFID functions are described, for example, in Penuela U.S. Pat. No. 5,493,805, Mosher U.S. Pat. No. 5,457,906, Mosher U.S. Pat. No. 5,973,600, Beigel U.S. Pat. No. 5,973,598, Beigel U.S. Pat. No. 6,181,287, Peterson U.S. Pat. No. 5,479,797, and Peterson U.S. Pat. No. 5,581,924.
Bands are advantageous over other forms of ID cards containing data (such as credit cards, tickets or the like) since they can be attached to the wearer physically securely. As a result, current uses of identification bands include patient identification in hospitals, clinics and other locations; access in amusement parks; temporary security measures, facility access control, and ticketing and entitlement functions.
One important use for identification bands is patient identification and location in hospitals, clinics and other locations. When used in conjunction with an appropriate reader, patient information can be collected electronically and used by the medical staff in performance of their duties. Another example is to track the location of personnel such as convicts in a prison.
Identification bands provide information simply, for example, by a person visually reading printed information, or scanning barcode information, on the band or by electronically reading identification information transmitted by the identification band. Thus, barcodes, RFID devices and the like are used to enhance the information storage and data transfer of information associated with the band and the associated person or object. However, when an identification band transmits information to another device or receives information from another device, the accuracy of the information may be compromised by poor transmission.
Information is stored electronically in a transponder or RFID “tag” and that information is communicated to a tag “reader.” Communication between the RFID tag and reader is by the transmission and reception of electromagnetic (EM) waves, and each must have an antenna to convert electrical signals to EM waves and vice versa.
Low power RFID systems can operate over a wide range of frequencies, including the high-frequency (HF) through super-high-frequency (SHF) radio bands, roughly 3 Megahertz (MHz) to 6 Gigahertz (GHz). The performance of an RFID tag operating in the high frequency (HF) band, for example at 13.5 MHz, is generally not affected by the tag's proximity to the human body. This is desirable for RFID tags used in identification bands. Coupling between the tag antenna and the reader antenna is primarily by the magnetic component of the reactive near field, in which the tag antenna is configured as a coil in a resonant circuit. However, a typical wristband is six inches in length, which must include an antenna, while the wavelength at 13.5 MHz is 73 feet, and it is well known that antennas which are a small fraction of a wavelength in linear dimensions are very inefficient radiators and receptors. As a result, the useful range of operation may be very limited and sometimes can be just a few inches from the reader antenna. This is a significant disadvantage which may limit the usefulness of HF tags in identification bands and may render them unusable, for example, in personnel location or ingress/egress alarm applications.
RFID systems may also operate at much higher frequencies, including operation at or in the vicinity of 400 MHz, 915 MHz, 2.45 GHz in the ultra-high frequency (UHF) band and 5.88 GHz in the SHF band. At these frequencies, coupling between the tag and reader antennas is by the radiating far field, which is the electromagnetic (EM) wave that propagates over distances of more than a few wavelengths. These frequencies correspond to wavelengths from 30 inches down to 2 inches, which are much more suitable, in terms of efficiency, for antennas in a band or other structure of comparable size. As a result of the more efficient antennas, operation at these frequencies may result in substantially higher ranges, typically up to ten feet or more. However, compared to the HF band, the radiation and reception of EM waves at these higher frequencies bands are affected much more strongly by obstacles and materials in the immediate environment of the antenna as a result of the shorter wavelengths. In particular, a loop or dipole antenna, operating on or adjacent to the human body, for example in a band, will be severely detuned and possibly rendered inoperable, with a commensurate degradation of the communication link. Thus the usability of these antennas in identification-bands with RFID capability is very limited.
The aforementioned antenna detuning and communication degradation problems are directly attributable to the fact that an isolated (free of nearby obstacles) loop or dipole antenna normally radiates EM energy in opposite directions. But, when on or near the surface of a human body, the reactive near fields (the electric and magnetic fields closest to the antenna) are distorted by the human tissue, causing an impedance mismatch between the antenna and the circuit to which it is immediately connected. This mismatch effectively detunes the antenna and reduces the amount of EM energy radiated in the direction away from the human body.
Therefore, there is a need for an improved antenna for an identification band.